1. Field of the Invention
The present invention relates to elastomer-coated bias fabrics of the type employed as reinforcement in such industrial products as power transmission belts, hoses, tires and the like and, more particularly, to a process for manufacturing such fabrics in which the fabric is transversely stretched on a tenter frame while the elastomer is applied to it.
2. Prior Art Statement
Bias-cut fabrics which have previously been coated and impregnated with an uncured, tacky, elastomeric compound, such as a synthetic elastomer, have conventionally been used in the production of power transmission belts, hoses, and the like as a protective cover and reinforcement. It is the common practice to combine the pre-coated bias-cut fabric with the carcass, substrate, or core of the product during the vulcanizing operation, such that heating cures and adhesively bonds the fabric to the rubber base of the product.
Elastomer-coated bias-cut fabrics have been the subject of a number of U.S. patents including:
U.S. Pat. No. 1,323,212, (1919) to Bulley PA1 U.S. Pat. No. 3,784,427, (1974) to Griffin PA1 U.S. Pat. No. 3,832,210, (1974) to Rohlfing PA1 U.S. Pat. No. 4,283,455, (1981) to McGee. PA1 U.S. Pat. No. 4,062,989, (1977) to Long PA1 U.S. Pat. No. 4,116,159, (1978) to Long PA1 U.S. Pat. No. 4,205,559, (1980) to Long et al.
as well as the following U.S. patents to Delmar D. Long, the inventor herein:
Bulley discloses a rubber impregnated bias cut fabric for use in a tire carcass. The Bulley fabric is prepared by a calendaring process.
Griffin discloses a method and apparatus for manufacturing an elastomer-coated bias cut fabric wherein a tubular woven fabric is cut spirally at a 45.degree. angle to produce a continuous sheet of fabric which is immersed in a curable binder and transversely stretched on a tenter frame to increase the complementary angle of the warp and weft threads. The binder is cured or otherwise hardened to stabilize the fabric and is subsequently immersion coated with a solution of an elastomer, such as neoprene dissolved in toluene. Thereafter the fabric is dried and cut into strips for application to V-belt cores.
McGee discloses a process which parallels that of Griffin wherein the fabric is coated with an elastomeric composition and then coated with additional elastomer. The details of the additional coating step are not disclosed in the patent, but the fabric is not transversely stretched until after the elastomer has been applied at the additional coating station.
Rohlfing discloses a bias cut fabric which is manufactured from a tubular fabric woven such that when the fabric is cut on the 45.degree. bias there is a minimum of selvage.
Long '989 discloses a method and apparatus for uniformly coating and impregnating a bias-cut woven fabric with a tacky elastomer. The fabric is coated while the fabric is pantographed and maintained in a transversely stretched condition on a tenter frame by sequentially applying a viscous elastomeric coating to the lower and upper surfaces of the fabric inwardly of the edges and by smoothing the coatings to a uniform thickness. It has been known to apply the elastomer to the lower surface of the fabric using an idle roll coater, i.e., a roll coater which is driven solely by the movement of the fabric over the surface of the roll.
Long '559 is directed to a neoprene coating composition useful in the Long '989 process wherein a carboxylated neoprene is tackified with a high boiling aromatic oil.
Long '159 is directed to a coating head for applying viscous coatings such as elastomeric latices to a moving woven web. The coating head employs a pair of elongate manifolds extending across the web which simultaneously coat both faces of the web by extrusion and thereby ensure penetration of the interstices of the fabric by the coating composition. The patent teaches that the supply of coating material to the heads may be varied and that for some webs and coating compositions, the composition can be supplied from the bottom manifold alone and forced up through the web into the upper manifold where it forms a reservoir from which it is applied to the top surface of the fabric.
One of the principal advantages of the process described in Long '989 is its versatility. The process can be adapted to produce fabrics having a wide range of performance characteristics because the fabric is coated in a stretched and supported condition on the tenter frame. By contrast, in processes such as the McGee and Griffin processes, in which the elastomers are applied to the fabric by immersing the fabric in a bath of the elastomer, the coatings applied to each face of the fabric must be the same and the amount of elastomer applied to the fabric and the position of the elastomer on the fabric can only be varied to a limited degree. When the fabric is coated on the tenter frame as taught in Long '989, if desired, different coatings can be applied to each surface of the fabric, the amount of elastomer applied to each surface of the fabric can be adjusted, and the position of the elastomer on the fabric can be controlled. In addition, if desired, the yarn angle can be varied.
3. Discussion of Cross-Referenced Applications
Commonly assigned U.S. patent application Ser. No. 350,969 (now U.S. Pat. No. 4,501,771) and Ser. No. 533,098 (now U.S. Pat. No. 4,490,428), of which this application is a combined continuation-in-part, are incorporated herein by reference. These applications describe processes for manufacturing elastomer-coated fabric in which, after pre-impregnating the fabric with a yarn lubricating composition, a non-tacky latex is applied to both surfaces of the fabric. Downstream, after drying the elastomeric coating, the elastomer on one surface of the fabric is overcoated with a tackified latex. The tackified latex composition is not applied to both sides of the fabric because such latices can bond to mold surfaces when the fabric is cured to a rubber body (such as in the manufacture of a V-belt) and this makes the fabric coated body very difficult to remove from the mold.
In the processes described in the aforementioned applications, a non-tacky elastomer is applied to both sides of the fabric. Typically this is accomplished using a top and a bottom coater but the applications also disclose that the coating can be applied to one surface of the fabric and forced through the fabric to the opposite surface. The latter technique is, however, acknowledged to be a difficult means for producing smooth and uniform coatings.